U.S. patent number 5,455,014 [Application Number 08/094,817] was granted by the patent office on 1995-10-03 for liquid deposition source gas delivery system.
This patent grant is currently assigned to Hughes Aircraft Company. Invention is credited to Michael A. Costantino, William C. Yorke.
United States Patent |
5,455,014 |
Costantino , et al. |
October 3, 1995 |
Liquid deposition source gas delivery system
Abstract
A liquid deposition source delivery system (22) includes a
reactant source (50) of a liquid chemical reactant, a first heater
(54) positioned adjacent to the reactant source (50) , and a vapor
collection system (56) in communication with the reactant source
(50) to collect vapor evolved from the reactant source (50). A flow
controller (64) has an upstream side (66) in communication with the
vapor collection system (56). A line (70) of a vapor distribution
system is in communication with the downstream side (68) of the
flow controller (64). A second heater (76) is positioned adjacent
to the flow controller (64), at least a portion of the vapor
collection system (56), and at least a portion of the vapor
distribution system, to prevent the vapor from condensing in the
lines (70) of the delivery system. One purge system (94) is used
for the upstream side of the flow controller (64) and the vapor
collection system (56), and a second purge system (96) is used for
the downstream side of the flow controller (64) and the lines (70)
of the vapor distribution system.
Inventors: |
Costantino; Michael A. (San
Marcos, CA), Yorke; William C. (Vista, CA) |
Assignee: |
Hughes Aircraft Company (Los
Angeles, CA)
|
Family
ID: |
22247356 |
Appl.
No.: |
08/094,817 |
Filed: |
July 20, 1993 |
Current U.S.
Class: |
422/305; 122/5;
137/334; 137/341; 392/388; 392/394; 392/396; 392/400; 422/110;
422/198; 422/199; 422/202; 422/244; 422/285; 422/307 |
Current CPC
Class: |
C23C
16/448 (20130101); Y10T 137/6606 (20150401); Y10T
137/6416 (20150401) |
Current International
Class: |
C23C
16/448 (20060101); A61L 009/00 (); G05D 007/00 ();
F28D 007/00 (); F16K 049/00 () |
Field of
Search: |
;422/106,110,198,199,202,244,255,285,288,290,305,307
;392/388,394,396,397,400,319,324 ;122/5 ;137/334,341 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Warden; Robert J.
Assistant Examiner: Kim; Christopher Y.
Attorney, Agent or Firm: Schubert; W. C. Denson-Low; W.
K.
Claims
What is claimed is:
1. A liquid deposition source delivery system, comprising:
a reactant source of a liquid chemical reactant;
a first heater positioned adjacent to the reactant source;
a vapor collection system in communication with the reactant source
to collect vapor evolved from the reactant source;
a flow controller having an upstream side in communication with the
vapor collection system and a downstream side;
a vapor distribution system in communication with the downstream
side of the flow controller; and
a second heater positioned adjacent to the flow controller, the
vapor collection system, and the vapor distribution system, the
second heater being operable to heat an entire vapor flow path from
the reactant source to a remote termination of the vapor
distribution system.
2. The delivery system of claim 1, further including
a first gas purge system in communication with the vapor collection
system and the upstream side of the flow controller.
3. The delivery system of claim 2, wherein the first gas purge
system comprises:
a purge gas source having a purge gas source outlet,
a pressure regulator having a pressure regulator inlet in
communication with the purge gas source outlet, and having a
pressure regulator source outlet, and
a first purge flow controller having a first purge flow controller
inlet in communication with the pressure regulator outlet, and a
first purge flow controller outlet in communication with the vapor
collection system and the upstream side of the flow controller.
4. The delivery system of claim 1, further including
a second gas purge system in communication with the vapor
distribution system and the downstream side of the flow controller,
the communication being direct and not through the flow
controller.
5. The delivery system of claim 4, wherein the second gas purge
system comprises:
a purge gas source having a purge gas source outlet, and
a second purge flow controller having a second purge flow
controller inlet in communication with the purge gas source outlet,
and a second purge flow controller outlet in communication with the
vapor distribution system and the downstream side of the flow
controller.
6. The delivery system of claim 1, further including
an additional reactant source of an additional liquid chemical
reactant;
an additional first heater positioned adjacent to the additional
reactant source;
an additional vapor collection system in communication with the
additional reactant source to collect vapor evolved from the
additional reactant source;
an additional flow controller having an upstream side in
communication with the additional vapor collection system and a
downstream side; and
an additional vapor distribution system in communication with the
downstream side of the additional flow controller;
and wherein the second heater is positioned adjacent to the
additional flow controller, at least a portion of the additional
vapor collection system, and at least a portion of the additional
vapor distribution system.
7. The delivery system of claim 1, wherein the flow controller
includes a mass flow controller.
8. The delivery system of claim 1, wherein the second heater
includes
a first heating tape wrapped onto the vapor collection system,
a second heating tape wrapped onto the vapor delivery system,
and
a conductive heater adjacent to the flow controller.
9. A liquid deposition source delivery system, comprising:
means for supplying a flow of a vapor having a boiling point
greater than ambient temperature;
means for controlling the flow of the vapor, the means for
controlling having an upstream side in communication with the means
for supplying and a downstream side;
means for distributing a flow of the vapor, the means for
distributing being in communication with the downstream side of the
means for controlling the flow of the vapor; and
second purging means for purging at least a portion of the means
for distributing and at least a portion of the means for
controlling the flow of the vapor, the second purging means being
connected to the means for distributing such that a purge gas can
flow from the second purging means to the means for distributing
without passing through the means for controlling.
10. The delivery system of claim 9, further including
first purging means for purging at least a portion of the means for
supplying and at least a portion of the means for controlling the
flow of the vapor.
11. The delivery system of claim 10, wherein the first purging
means comprises:
means for supplying a purge gas, the means for supplying having a
purge gas source outlet,
means for regulating the pressure of the purge gas received from
the means for supplying, and
means for controlling the flow of the purge gas received from the
means for supplying.
12. The delivery system of claim 9, wherein the second purging
means comprises:
means for supplying a purge gas, the means for supplying having a
purge gas source outlet, and
means for controlling the flow of the purge gas received from the
means for supplying.
13. The delivery system of claim 9, further including:
means for heating at least a portion of the means for supplying,
the means for controlling the flow of the vapor, and at least a
portion of the means for distributing.
14. A liquid deposition source delivery system, comprising:
a reactant source of a liquid chemical reactant;
a first heater positioned adjacent to the reactant source;
a vapor collection system in communication with the reactant source
to collect vapor evolved from the reactant source;
a flow controller having an upstream side in communication with the
vapor collection system and a downstream side;
a vapor distribution system in communication with the downstream
side of the flow controller;
a second heater positioned adjacent to the flow controller, at
least a portion of the vapor collection system, and at least a
portion of the vapor distribution system;
a first gas purge system in communication with the vapor collection
system and the upstream side of the flow controller; and
a second gas purge system in communication with the vapor
distribution system and the downstream side of the flow
controller.
15. The delivery system of claim 14, wherein the first gas purge
system comprises:
a purge gas surface having a purge gas source outlet,
a pressure regulator having a pressure regulator inlet in
communication with the purge gas source outlet, and having a
pressure regulator source outlet, and
a first purge flow controller having a first purge flow controller
inlet in communication with the pressure regulator outlet, and a
first purge flow controller outlet in communication with the vapor
collection system and the upstream side of the flow controller.
16. The delivery system of claim 14, wherein the second gas purge
system comprises:
a purge gas source having a purge gas source outlet, and
a second purge flow controller having a second purge flow
controller inlet in communication with the purge gas source outlet,
and a second purge flow controller outlet in communication with the
vapor distribution system and the downstream side of the flow
controller.
17. The delivery system of claim 14, further including
an additional reactant source of an additional liquid chemical
reactant;
an additional first heater positioned adjacent to the additional
reactant source;
an additional vapor collection system in communication with the
additional reactant source to collect vapor evolved from the
additional reactant source;
an additional flow controller having an upstream side in
communication with the additional vapor collection system and a
downstream side; and
an additional vapor distribution system in communication with the
downstream side of the additional flow controller;
and wherein the second heater is positioned adjacent to the
additional flow controller, at least a portion of the additional
vapor collection system, and at least a portion of the additional
vapor distribution system.
Description
BACKGROUND OF THE INVENTION
This invention relates to the deposition of thin layers from
reactive gases, and, more particularly, to a system for delivering
such gases to a deposition reactor.
In chemical vapor deposition (CVD), one or more reactive gases is
contacted to a substrate that has been energized, as by heating.
With the proper selection of the reactive gas or gases, the
substrate type and temperature, gas partial and total pressures,
and other operating parameters, the reactive gases deposit a
selected material as a gradually thickening layer onto the surface
of the substrate. The deposition continues until the desired
thickness is reached.
The reactive gases used in the reactive deposition are provided
from either gaseous or liquid sources. Liquid sources have become
increasingly popular, as the reactive gases are often safer to
handle and less toxic when provided in their liquid forms. Prior to
the reactive deposition, the liquid source is heated to produce a
vapor of the reactive gas, which is conducted to the substrate and
reacted.
Several heretofore unsolved problems have been encountered in
delivery systems that utilize liquid sources of the reactive gases.
Flow variations in individual gases are sometimes observed, leading
to variations in composition of the deposited layer. Deposits can
build up in the interior of the delivery system. Contaminants can
enter the system during operating transitions such as the changing
of sources. Although acceptable deposited structures can often be
made in spite of these problems, it would be preferred to improve
deposition and delivery system operation through their
solution.
There is therefore a need for an improved reactive gas delivery
system for use with liquid sources. The present invention fulfills
this need, and further provides related inventions.
SUMMARY OF THE INVENTION
The present invention provides a gas delivery system operating from
at least one liquid source, for use in reactive gas deposition
procedures such as chemical vapor deposition. The gas delivery
system minimizes the introduction of contamination during
changeovers and at other times. Flow variations are also largely
avoided by preventing the deposition of unreacted vapor in the gas
delivery system. The absence of contamination and the avoidance of
the deposition of unreacted vapor prevents the buildup of
contamination deposits within the gas delivery system. The gas
delivery system of the invention is compatible with the use of
high-precision controllers such as mass flow controllers,
permitting careful control of the composition of the deposited
layers.
In accordance with the invention, a liquid deposition source
delivery system comprises means for supplying a flow of a vapor
having a boiling point greater than ambient temperature and means
for controlling the flow of the vapor. The means for controlling
has an upstream side in communication with the means for supplying
and a downstream side. The apparatus also includes means for
distributing a flow of the vapor, which is in communication with
the downstream side of the means for controlling the flow of the
vapor. There is a means for heating at least a portion of the means
for supplying, the means for controlling the flow of the vapor, and
at least a portion of the means for distributing.
In another embodiment, a liquid deposition source delivery system
comprises a reactant source of a liquid chemical reactant, and a
first heater positioned adjacent to the reactant source. A vapor
collection system is in communication with the reactant source to
collect vapor evolved from the reactant source. A flow controller
has an upstream side in communication with the vapor collection
system and a downstream side. The apparatus includes a vapor
distribution system in communication with the downstream side of
the flow controller. A second heater is positioned adjacent to the
flow controller, at least a portion of the vapor collection system,
and at least a portion of the vapor distribution system.
The second heater, also called the means for heating, prevents
reactive gas previously vaporized from the reactant source from
depositing in the flow controller, the vapor collection system, and
the vapor distribution system. These components are heated to a
temperature above the boiling point of the reactive gas flowing in
that portion of the system. The reactive gas therefore cannot
deposit prior to reaching a reactor.
To minimize contamination, there is preferably provided a two-part
purge system. The purge system includes a first gas purge system in
communication with the vapor collection system and the upstream
side of the flow controller and/or a second gas purge system in
communication with the vapor distribution system and the downstream
side of the flow controller. In the preferred approach, both the
first and second purge systems are provided, to prevent
contaminants from entering the gas delivery system during transient
conditions such as source changeovers, and to clean contaminants
from the delivery system if they do reach it.
The present invention provides an advance in the art of gas
delivery systems, particularly those for use in reactive deposition
procedures such as chemical vapor deposition. Other features and
advantages of the present invention will be apparent from the
following more detailed description of the preferred embodiment,
taken in conjunction with the accompanying drawings, which
illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a reactive gas deposition system;
and
FIG. 2 is a more detailed schematic diagram of the gas delivery
portion of the deposition system of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a reactive gas deposition system 20 in which the
present invention is used. FIG. 2 illustrates a portion of the
deposition system 20, the gas delivery system 22 of the invention,
in more detail. These systems 20 and 22 are illustrated with
various combinations of gas flow sources and deliveries utilized in
a preferred embodiment. The present invention is not limited to
these particular combinations.
The reactive gas deposition system 20 includes a reactor 24,
typically in the form of a quartz tube, that is heated by a furnace
26 around the reactor 24. A substrate 28, upon which the reactive
gas deposition product is to be deposited, is supported within the
reactor by a fixture 30.
Reactive gases and other gases are provided to the reactor 24
through one or more delivery gas lines 32. The delivery gas lines
32 extend from the gas delivery system 22 to the reactor 24. The
reactive gas or gases enter the heated reactor 24, mix together
within the reactor 24, and deposit the desired solid layer onto the
surface of the substrate 28. In the preferred embodiment, there are
three delivery gas lines 32, labelled DG1, DG2, and DG3 for
subsequent reference.
The unreacted portion of the reactive gases and any gaseous
reaction products leave the reactor 24 through an exit line 34 and
enter a gas cleanup and exhaust system 36. In the gas cleanup and
exhaust system 36, particulate matter in the gas is removed and any
unreacted gases are reacted so that there is diminished tendency
for downstream deposition of solids. After the completion of the
gas cleanup, the gas is exhausted.
Gases are delivered to the gas delivery system from a gas source 38
through source gas lines 40.
The present invention is concerned with the gas delivery system 22
and to some extent its relation with the delivery gas lines 32, the
source gas lines 40, and the gas source 38. The relevant structures
are discussed in greater detail in relation to FIG. 2. The details
of the construction of the reactor 24, the furnace 26, and the gas
cleanup and exhaust system 36 are known in the art for conventional
systems, and do not form a part of the present invention. They are
presented here only to show the context of the use of the present
invention.
FIG. 2 presents the schematic flow diagram for a preferred form of
the gas delivery system 22. In the system of FIG. 2, several
different types of gases are provided and combined in different
ways, to illustrate some possibilities of the system. In each case,
reactive gases flow from a source, of which there are liquid and
gaseous types. In a liquid source 50, a container 52 of the liquid
is maintained at a preselected vaporization temperature by a
heating system 54. The heating system 54 preferably includes a
combination of heating and cooling coils and a thermostat. Such
heating systems 54 are available commercially, the presently
preferred heating system 54 being the Schumaker heating system
model STC 115.
A vapor collection system 56 captures the gaseous vapor evolved
from the liquid source 50. In some types of liquid sources, the
reactive gas vapors alone are captured and conducted to the
reactor. In other types of liquid sources, an inert carrier gas
such as argon is bubbled through the container 52, and the vapor is
mixed with the carrier gas to be carried to the reactor. This
latter type of liquid source is not preferred in the present
invention, but is illustrated in one of the liquid sources of FIG.
2 with a carrier gas line 57 to show the general applicability of
the present invention. Three separate liquid sources 50 are shown
in FIG. 2. A gaseous source 58 preferably includes a pressurized
gas bottle 60 and a regulator 62. Gas flowing from the gaseous
source 58 is conducted in the vapor collection system 56.
The vapor collection system 55 includes the source gas lines 40
extending from the liquid source 50 or gaseous source 58 to a mass
flow controller ("MFC") 64. In the illustrated case, there are four
sources 50 and 58, and therefore four source gas lines 40, SG1,
SG2, SG3, and SG4. The MFC 64 is an available commercial unit which
accurately and controllably establishes the mass flow of each gas
type to the reactor 24. The Unit Instruments Model 1200 and Vacuum
General Model LC2 are preferred. The source gas lines 40 enter an
upstream side 66 of the MFC 64 and exit a downstream side 68. In
some instances, as shown here for the case of the gaseous source
58, a single source can supply gas to more than one mass flow
controller.
From the downstream side 68 of the MFC 64, the gas flows through
gas delivery system internal lines 70 to a shutoff valve 72 that
can isolate each respective gas source 38 and MFC 64 from the
remainder of the gas delivery system 22 and reactor 24. The shutoff
valves 72 are of particular use when sources or controllers are to
be changed.
In some cases, the reactive gas from the source flows directly to
the reactor 24 and is mixed with the other reactive gases in the
reactor. In other cases, it is preferred to mix combinations of
reactive gases prior to their entering the reactor, and then to mix
these combination mixes in the reactor. In the present
illustration, two pairs of the reactive gases are mixed within the
gas delivery system 22, at mixing locations 73 where there is a
confluence of flows in two lines 70. This particular illustrated
arrangement results in three delivery gas lines 32 extending from
the gas delivery system 22 to the reactor 24, lines DG1, DG2, and
DG3. Other requirements for gas delivery will result in other
mixing combinations and delivery gas line arrangements.
To prevent recondensation of the vaporized gases from the sources
50 before they reach the reactor 24, heating means is provided to
heat at least a portion of the system that supplies the gas to the
reactor after it leaves the gas sources. In the illustrated
embodiment, there are two types of heaters in the heating means. To
aid in heating the components of the gas delivery system 22 such as
the MFCs 64, the valves 72, the lines 70, and other apparatus,
these components are mounted on a support base 74. The preferred
support base 74 is a thermally conductive block of metal, such as
an aluminum alloy. For the gas delivery system 22 shown in FIG. 2,
the support base 74 was an aluminum alloy block about
24.times.24.times.1.5 inches in size, but the size will vary
according to the number of components to be mounted thereon.
The support base 74 is heated by appropriate heaters 76 contacting
the support base 74, which by conduction heats the components
mounted thereon. In the preferred approach, the heaters are
cartridge heaters such as the Model CIR made by Omega. In FIG. 2,
only two of the heaters 76 are shown for clarity of
illustration.
The other type of heater for the gas delivery system and its
related lines is a heater for the lines 32 and 40. This heater is
preferably a heating tape 78 that is wrapped around the lines 32
and 40. Heating tape is a commercially available product, and a
preferred heating tape is the model QTVB available from Raythem.
The heating tape 78 is wrapped around the lines containing
condensable vapors produced in the sources 50, and optionally
around the lines that conduct gas from the gaseous source 58.
The heaters 76 and 78 are controlled by a temperature controller
80, to maintain the delivery system 22 and the lines 32 and 40 at a
temperature sufficiently high that the vapors flowing to the
reactor 24 do not condense. The controller 80 receives a
temperature feedback signal from temperature sensors 82 in the
block and temperature sensors 84 on the lines 32 and 40. The
controller 80 compares the measured temperatures with that set by a
set point input 85 on the controller 80, and supplies heat through
the heaters 76 and 78 accordingly. The power lines 86 and 88,
respectively, for the heaters 76 and 78 operate from power supplies
in the temperature controller 80. (Only a few of the temperature
sensors and power lines are shown in FIG. 2 for the sake of clarity
in illustration.)
A gas delivery purge system 90 prevents unwanted contaminants from
reaching the reactor 24. The gas delivery purge system 90 includes
a purge gas source 92 of a purge gas such as nitrogen. The purge
gas source 92 supplies purge gas to a first gas purge system 94 and
a second gas purge system 96.
The first gas purge system 94 is in communication with the vapor
collection system 56 and the upstream side 66 of the mass flow
controller 64. It includes a low pressure regulator 98 that
controllably reduces the pressure in the system 94 to a very low
value for use in calibration work, and a flow meter 100 that serves
as a flow controller. Purge gas from the system 94 controllably
flows to the individual vapor collection systems 56 and mass flow
controllers 64 through valves 102. As illustrated, the purge gas
system 94 may be used on only some of the source lines, and not on
others. It is preferably used in conjunction with all liquid
sources 50 but optionally in conjunction with gas sources 58.
The first gas purge system 94 performs three important functions.
The first is to purge contaminants from the vapor collection system
56 and the upstream side 66 of the mass flow controller 64 when the
source 50 is changed. When a source 50 is to be changed, the valve
72 is closed and the valve 102 opened so that purge gas continually
flows through the affected portions of the system. Most of the flow
of potential contaminants into the gas delivery system 22 and
thence to the reactor 24 is thereby prevented. The second function
is to continue to purge contaminants from the affected portions of
the system after the valve 72 is reopened. This continuing purge
function is also used at other times, if there is reason to believe
that any deposits of condensed vapors or contaminants have
developed within the gas source lines 40 or the MFCs 64.
The third function of the gas purge system 94 is in the calibration
of the mass flow controllers. When a mass flow controller 64 is to
be calibrated, the purge gas system 94 is operated with the valves
72 and 102 open. The actual flow of the purge gas is established by
adjusting the regulator 98 and measured by the flow meter 100,
which is specifically calibrated for the particular purge gas. The
reading of the mass flow controller 64 is measured for various
values of the flow through the flow meter 100. The mass flow
controller 64 is calibrated to the flow rates of the specific
reactive gas vapor using these values and standard calibration
tables for the mass flow controller.
In conventional practice, when a mass flow controller is to be
calibrated, it is removed from the gas system and taken to a
separate calibration station. After calibration is complete, the
MFC is replaced in the system. This procedure is slow, particularly
where there are multiple MFCs, and introduces contaminants into the
gas system each time the lines are opened. As a result, calibration
is commonly deferred as much as possible, possibly leading to
inaccuracies in the mass flows reaching the reactor 24. With the
present approach, calibration is less onerous, and can be
accomplished readily and at any time other than when deposition
operations are actually underway.
The second gas purge system 96 includes a flow meter 104 that
controls and measures the flow of the purge gas. Access of the
purge gas to the various gas systems is controlled by valves 106.
The second gas purge system 96 communicates with the vapor
distribution distribution system in the form of the delivery gas
lines 32 and the downstream side 68 of the mass flow controller 64
through the valves 72 when open. The second gas purge system 96
permits the downstream portion of the gas delivery system to be
separately purged from the upstream portion. Separate purging is
desirable because the first gas purge system 94 can deliver only a
relatively slow purging flow through the MFC 64.
The reactive gas deposition system 20 of FIG. 1 with the gas
delivery system 22 of FIG. 2 has been built and operated. It is
highly effective in depositing high purity layers onto substrates
from gas and liquid sources. Contamination is reduced and
efficiency of operation is increased, as compared with conventional
systems.
Other features and advantages of the present invention will be
apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention.
* * * * *